Major hazard risk assessment over non-flat terrain. Part I: continuous releases

Hankin, R.K.S.. 2004 Major hazard risk assessment over non-flat terrain. Part I: continuous releases. Atmospheric Environment, 38 (5). 695-705.

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Liquefied gases, such as chlorine or ammonia, are stored in large quantities on industrial sites. If released accidentally, they can form a heavy gas cloud that has the potential to kill or injure large numbers of people. The dispersion of such a cloud is thus of interest to the risk assessment community. This is the first of a two-part paper. Here, the risk(probability) of being exposed to a continuously released toxic gas cloud, given a release, is considered; probability language is needed because wind direction is assumed to be a random variable. Part II considers instantaneous releases. Risk is considered in terms of RC; the probability at any point of receiving a non-zero dose given a continuous release. For flat ground, simple analytical techniques show that RCC32=3 2p F2=3 r1=3 u1 Q1=3 for a uniform windrose (windspeed u) at radius r due to a continuous release of buoyancy flux Q: Here F is the front Froude number. This paper shows how the riskof being exposed to heavy gas from a steady continuous release is affected by non-flat terrain, using the established shallow layer model TWODEE (Journal of Hazardous Materials 66(3) (1999a) 211). Results from both simple slopes and real terrain are presented. A range of windspeeds and slopes are considered. For a steady 44 kg s1 continuous release under a windspeed of 1 m s1; groundslopes as low as 2% can substantially affect the riskin the sense that the predicted risk contours are far from circularly symmetric. The real terrain data used is from Little Barrier Island, New Zealand (latitude 36110S; longitude 17540E), chosen on account of its being uninhabited, and having steep slopes and complex topography. As the windspeed increases from 1 to 10 m s1; riskcontours become less affected by terrain in that their complexity is reduced.

Item Type: Publication - Article
Digital Object Identifier (DOI):
ISSN: 1352-2310
Additional Keywords: Heavy gas dispersion, Major hazards, Risk assessment, Slopes, Complex terrain
Date made live: 19 Oct 2004 +0 (UTC)

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